The invention is generally directed to toner compositions, and more specifically, the present invention is directed to developer and toner compositions containing charge enhancing additives, which impart, or assist in imparting a negative charge to the toner resin particles. In one embodiment, there is provided in accordance with the present invention toner compositions comprised of resin particles, pigment particles, and zinc dithiolene complexes, such as bis(tetra-butylammonium), bis(1,3-dithiole-2-thione-4,5-dithiolate)zinc complex, which are available from American Tokyo Kasei, Inc. as negative charge enhancing additives. The aforementioned toner compositions usually contain pigment particles comprised of, for example, carbon black, magentites, cyan, magenta, yellow, blue, green, red, or brown components, and mixtures thereof thereby enabling their selection for the development of black and/or colored images. Additionally, the charge additives illustrated herein are believed to be nontoxic in that, for example, they are capable of generating an acceptable negative Ames test, and further there is provided with the present invention toner compositions with stable electrical properties for extended time periods exceeding, for example, 100,000 imaging cycles in some instances. Moreover, the toner and developer compositions of the present invention can be selected for electrophotographic, especially xerographic, imaging and printing processes.
Developer compositions with charge enhancing additives, which impart a positive charge to the toner resin, are well known. Thus, for example, there is described in U.S. Pat. No. 3,893,935 the use of quaternary ammonium salts as charge control agents for electrostatic toner compositions. There is also described in U.S. Pat. No. 2,986,521 reversal developer compositions comprised of toner resin particles coated with finely divided colloidal silica. According to the disclosure of this patent, the development of electrostatic latent images on negatively charged surfaces is accomplised by applying a developer composition having a positively charged triboelectric realationship with respect to the colloidal silica.
Also, there is disclosed in U.S. Pat. No. 4,338,390, the disclosure of which is totally incorporated herein by reference, developer compositions containing as positive charge enhancing additives organic sulfate and sulfonates. Further, there is disclosed in U.S. Pat. No. 4,298,672 positively charged toner compositions with resin particles and pigments particles, and as charge enhancing additives alkyl pyridinium compounds. Additionally, other documents disclosing positively charged toner compositions with charge control additives include U.S. Pat. Nos. 3,944,493; 4,007,293; 4,079,014 and 4,394,430.
Moreover, toner compositions with negative charge enhancing additives are known, reference for example U.S. Pat. Nos. 4,411,974 and 4,206,064, the disclosures of which are totally incorporated herein by reference. The '974 patent discloses negatively charged toner compositions comprised of resin particles, pigment particles, and as a charge enhancing additive ortho-halo phenyl carboxylic acids. There is disclosed in the '064 patent toner compositions with chromium, cobalt, and nickel complexes of salicylic acid as negative charge enhancing additives.
As a result of a patentability search, there were located U.S. Pat. Nos. 4,656,112 and 4,673,631. In the '112 patent, there are described toners for developing electrostatic latent images wherein there is selected as a charge control agent a zinc complex compound of aromatic hydroxy carboxylic acid with or without a substituent, reference the Abstract of the Disclosure. These toners may be negatively charged, reference column 2, lines 5 to 10. The formula of the zinc complex is represented in column 2, beginning at line 35. The '631 patent describes a triboelectrically chargeable toner composition, which contains a metal complex of an amino acid compound having an amino or amino substituted amino group, and a carboxylic acid, reference the Abstract of the Disclosure. Also, note the teachings in column 5, lines 5 through 18. Further, it is indicated in column 5, lines 40 to 42, of the '631 patent that the aforementioned metal complex can be a good positive charge controller.
There is illustrated in U.S. Pat. No. 4,404,271, the disclosure of which is totally incorporated herein by reference, a complex system for developing electrostatic images with a toner which contains a metal complex represented by the formula in column 2, lines 20 to 31; and wherein ME can be chromium, cobalt or iron. Additionally, other U.S. patents dislcosing various metal containing azo dyestuff structures wherein the metal is chromium or cobalt include 2,891,939; 2,871,233; 2,891,938; 2,933,489; 4,053,462 and 4,314,937. Also, in U.S. Pat. No. 4,433,040, the disclosure of which is totally incorporated herein by reference, there are illustrated toner compositions with chromium and cobalt complexes of azo dyes as negative charge enhancing additives.
Other prior art includes Japanese Publication No. 54-145542 which illustrates a negatively chargeable toner consisting of a resin, a colorant, and the charge control agent pyridoxine aliphatic acid ester; East German Patent Publication No. 218697 relating to liquid developers with charge control additives with structural units of formulas (I), (II) and (III), which contain olefinically polymerizable bonds; U.S. Pat. No. 3,850,642 relating to multilayer sensitive elements with ionizable salts, acids, esters, and surfactants as charge control agents; 2,970,802 illustrating a composition for the control of hypercholestermia, which composition consists of a nontoxic gelatin containing aluminum nicotinate; 3,072,659 which discloses a method of preparing aluminum salts of nicotinic acid; Japanese Publication No. 61/239443, which discloses bisphenyl dithiol transition metal complexes for optional recording; the Journal of Organic Chemistry, 1987, 52, 3285; and Molecular Crystal Liquid Crystals, 1982, 86, 159.
Furthermore, there is disclosed in copending application U.S. Ser. No. 822,186, the disclosure of which is totally incorporated herein by reference, toner compositions containing as negative charge enhancing additives iron complexes, including the iron complex of azo dyes prepared from coupling diazotized substituted amino phenols with substituted naphthols.
Although many charge enhancing additives are known, there continues to be a need for new additives, especially those that impart negative charges to toner resin particles. Additionally, there is a need for negative charge enhancing additives which are useful for incorporation into black, or colored toner compositions. There is also a need for toner compositions with negative charge enhancing additives that possess acceptable triboelectric charging characteristics, and suitable admixing properties. Moreover, there continues to be a need for humidity insensitive negatively charged toner and developer compositions. Further, there is a need for charge enhancing additives which can be easily and permanently dispersed into toner resin particles. There also is a need for negatively charged black and colored toner compositions that are useful for incorporation into various imaging processes, inclusive of color xerography, as illustrated in U.S. Pat. No. 4,078,929, the disclosure of which is totally incorporated herein by reference; laser printers; and additionally, the toner compositions of the present invention are useful in imaging apparatuses having incorporated therein layered photoresponsive imaging members, such as the members illustrated in U.S. Pat. No. 4,265,990, the disclosure of which is totally incorporated herein by reference. Furthermore, there is a need for negatively charged toner compositions with desirable and rapid toner admix charging characteristics of, for example, from about less than 2 minutes.